Lifetime Analysis-Modelling # 1995 Edinburgh
A plane strain specimen has been developed which creates a biaxial stress state when loaded in uniaxial tension. A detailed stress analysis of this specimen is presented. The stress state was generated though the use of a groove across the width of the specimen. Both theoretical and experimental results are presented. For polyethylene and similar polymers, the stress state in the groove section was approximately in the ratio 1 :2 which is nearly identical to the stress state in a pressurized pipe. Because of the identity of stress state, this simple specimen becomes a cost-effective and accurate means of predicting pipe long term performance without having to test the pipe itself. In addition to detailing the specimen design, results are presented for polyethylene pipe hydrostatically pressurized at various temperatures and compared to the plane strain tensile specimen tested also at various temperatures. It will be also shown that the best method for plotting creep rupture data is to use the Von-Mises calculated stress and nor simply pipe hoop stress. This specimen and technique wili be advocated as a standard method for evaluating pipe resins.